Background: Belinostat is a histone deacetylase inhibitor with anti-tumor effect in several pre-clinical tumor models and clinical trials. The aim of the study was to evaluate changes in cell proliferation and glucose uptake by use of 3’-deoxy-3’-[18F]fluorothymidine ([18F]FLT) and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) following treatment with belinostat in ovarian cancer in vivo models. Methods: In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) were studied after treatment with belinostat. Mice were divided in 2 groups receiving either belinostat (40 mg/kg ip twice daily Day 0–4 and 6–10) or vehicle. Baseline [18F]FLT or [18F]FDG scans were made before treatment (Day 0) and repeated at Day 3, 6 and 10. Tracer uptake was quantified using small animal PET/CT. Results: Tumors in the belinostat group had volumes that were 462 ± 62% (640 mm3) at Day 10 relative to baseline which was significantly different (P = 0.011) from the control group 769 ± 74% (926 mm3). [18F]FLT SUVmax increased from baseline to Day 10 (+30 ± 9%; P = 0.048) in the control group. No increase was observed in the treatment group. [18F]FDG SUVmean was significantly different in the treatment group compared to the control group (P = 0.0023) at Day 10. Within treatment groups [18F]FDG uptake and to a lesser extent [18F]FLT uptake at Day 3 were significantly correlated with tumor growth at Day 10. Conclusions: [18F]FDG uptake early following treatment initiation predicted tumor sizes at Day 10, suggesting that [18F]FDG may be a valuable biomarker for non-invasive assessment of anti-tumor activity of belinostat.